The invention relates to an electrical apparatus with electronic control, permanently supplied with AC or DC, and an operating mode of which can be triggered by the application of the supply voltage to a control input of the apparatus.
A typical example of apparatus covered by the invention is a timer which is normally continuously supplied with power, and which closes or opens a relay for a defined duration after the closure of an electrical control contact which applies the supply voltage (the mains at 230 volts, for example) onto the control input of the timer. Or else a timer which closes or opens a relay after a defined duration has elapsed after the closure of this control contact.
However, the invention may be applied to much other electrical apparatus, wherever a functionality of this apparatus is triggered by the application, to a control input, of a voltage which is the voltage permanently supplying the apparatus.
FIG. 1 represents the general principle of the apparatus which it is desired to produce, and it will be considered, in what follows, that it is a timer that is involved.
The apparatus AP includes two permanent external power-supply terminals A and B intended to receive an AC voltage (mains voltage at 230 volts, for example) or a DC voltage (for example 12 volts or 24 volts).
The apparatus also includes a control input E and, if the functionality of the apparatus requires it, output terminals, here S1, S2, S3. In this example, S1, S2, S3 are the output terminals of a relay internal to the apparatus.
The control input E triggers the operation of the apparatus if it is taken to the potential of the power-supply terminal B, for example by the closing of a contact SW linked between E and B. This contact SW may be a mechanical or electronic switch. A load LD has been represented, moreover, in FIG. 1, placed in parallel between the terminal A and the control input E, this load therefore consuming a current whenever the input E ceases to be at the potential of A, for example if the input E is taken to the potential of B. To give an idea, the load LD may quite simply be a pilot lamp which shows that the timer has been triggered.
This load linked to the control input E complicates the design of the internal control circuits of the apparatus as a result of the leakage currents which flow in this load when the contact SW is open. One object of the invention is to propose a control circuit which functions even in the event that this load is present.
Another object of the invention is to propose a control circuit which functions for various values of power-supply voltage of the apparatus, that is to say which can be connected directly to the power-supply voltage whatever the level thereof within a wide range of values.
In the prior art, apparatus such as that of FIG. 2 has been proposed, in which the apparatus contains an internal electronic circuit CE providing the desired functionality (control of the timing duration and control of the output relay, for example) and operating at low DC voltage Vdd (5 volts, for example). The internal electronic circuit then includes a detection input DT and the observation of the voltage level on this input DT allows the triggering of the desired operation of the apparatus. The voltage Vdd is derived from a rectification, filtering and regulation circuit RD. The control input E of the apparatus is linked to the detection input DT via a rectifier diode D and a resistor R. A voltage-level regulation and filtering circuit can be placed in parallel between the detection input DT and the 0 reference potential of the power supply Vdd. When the external contact SW is closed, the detection input DT receives a detectable signal which triggers the timer.
This solution has the drawback of being usable only for apparatus operating with a single possible power-supply voltage (for example 230 volts AC), since the value of the resistor R has to be matched to each power-supply voltage.
The voltage level on the detection input DT, after the contact SW has been closed, has in fact to be defined precisely in order for the circuit to function correctly.
Moreover, this solution also exhibits the drawback of a coupling between the external power supply and the detection input DT via the load LD when the contact SW is open, and this coupling is undesirable.
Apparatus has also been proposed, such as that of FIG. 3, using a photocoupler in order to provide DC isolation between the control input E and the detection input DT. The control input E is linked to a series assembly of a rectifier diode D, a current limiter SC and the input of a photocoupler PH. This series assembly is linked, furthermore, to the power-supply terminal A, and the photocoupler is activated when the control input E is taken to the potential of the terminal B via the contact SW. The output of the photocoupler PH is linked in series between the power-supply voltage Vdd of the internal electronic circuit CE, on the one hand, and the detection input DT, on the other hand. The rectification, filtering and regulation circuit RD, which produces the voltage Vdd, is identical to that of FIG. 2. A filtering circuit can also be placed in parallel between the detection input DT and the reference potential at 0 volts.
This circuit of FIG. 3 can function with a power-supply voltage having several possible levels (at least if the rectification, filtering and regulation circuit RD allows it). However, it is expensive because of the photocoupler and its current limiter.
The present invention proposes a different construction, not using a photocoupler, based on the use of half-wave rectification to produce the low-voltage DC Vdd, of a resistive divider bridge to apply this low voltage to the detection input DT, and digital processing making it possible to deduce the position of the contact SW from the shape of the signal present on the detection input DT, even in the case where an external load LD is connected to this contact.
According to the invention, on the one hand, the low voltage Vdd produced in order to supply the internal electronic circuits is established on the conductor linked to one of the power-supply external terminals (the one which is additionally linked to the contact SW); on the other hand, the resistive divider bridge, the intermediate point of which is linked to the detection input DT, is placed in series between the control input of the apparatus and the 0-volt reference potential of the low-voltage Vdd DC power supply. Thus, when the contact SW is closed, the potential Vdd is reinjected onto the detection input DT via the divider bridge. Conversely, when the contact SW is open, the resistive divider bridge is no longer supplied, but remains linked to the 0-volt reference potential in order to keep the detection input DT at zero.
In summary, the present invention proposes an electrical apparatus having two external power-supply terminals and including an electrical circuit accomplishing a defined function under the control of the closing or opening of an electrical contact capable of being linked between a first one of the external power-supply terminals and a control input, the apparatus further including:
an electronic decision circuit supplied by two conductors, one of which is at reference potential and the other of which is at a low DC voltage Vdd, the decision circuit having a signal-detection input and an output which is capable of taking up two states depending on the nature of the signal present on the detection input, this output controlling the said defined function of the electrical circuit,
a low-voltage DC power-supply circuit, itself supplied via the two external power-supply terminals, this circuit carrying out half-wave rectification and having the conductors at the reference potential and at the voltage Vdd as its outputs,
the apparatus being characterized in that:
a) the conductor at the voltage Vdd is linked to an external power-supply terminal,
b) the control input of the apparatus is linked by a first resistor R1 to the detection input of the decision circuit,
c) the detection input is linked by a second resistor R2 to the conductor at the reference potential,
d) the decision circuit includes electronic means for,
on the one hand, detecting the presence on the detection input of an alternating signal or of the reference potential, and then for putting the output into a first state,
and, on the other hand, detecting the presence, on the detection input, of a DC potential other than the reference potential, and then for putting the output into a second state.
The decision circuit will preferably consist of a microcontroller which can accomplish other functions in the apparatus and which, for the requirements of the invention, includes a program for testing the voltage level present on the detection input, and for comparing this voltage with a predetermined threshold, the program including a periodic test and causing the output to change to the second state if n successive tests show that the voltage level exceeds the predetermined threshold, n being a number chosen as a function of the period of the tests and of the period of the AC mains likely to supply the apparatus (50 Hz and/or 60 Hz especially).